A 2-alkene product having high purity is a product that can be utilized as a feedstock to make various other chemical compounds. There is a need in the industry to provide a process to convert an alkene-containing feed stream to a high purity 2-alkene product.
More specifically, there is a need in the chemical industry to produce a 2-butene (cis, trans, and mixed) product having a purity of about 99% for a number of reasons. The 2-butene product can be utilized to produce propylene via olefin metathesis with ethylene. High purity cis and/or trans 2-butene is also as starting materials for lubricants and agricultural chemicals.
The 1-butene containing feed stream used to produce the 2-butene product has typically been commercially available from mixed butene streams from refineries. Recently, the ability to meet the 2-butene product demand has suffered due to deterioration of the quality of available mixed butene streams. Specifically, the percentage of n-butane in the mixed butene streams has increased substantially, and the presence of this n-butane has limited the amount of 2-butene product that can be recovered via fractionation.
Generally, the mixed butene streams produced from refinery catalytic crackers are a mixture of butenes, isobutylene and butadiene. The isobutylene is usually separated from the butenes, and the 1-butene is isomerized to 2-butene prior to alkylation. Since there is about 1 to 2 wt % butadiene in these mixed butene streams, simple acid catalysis is not viable for refinery butene isomerization due to rapid coking caused by the presence of the butadiene. Phillips Petroleum Company developed and licensed the HYDRISOM® process for these refinery streams in the 1960s. The HYDRISOM® process employs an alumina catalyst with a slight loading of noble metal. A stoichiometric amount of hydrogen is simultaneously fed with the mixed butene stream, and the butadiene is selectively hydrogenated. The alumina catalyst isomerizes the 1-butene to 2-butene.
In recent years, the quality of the mixed butene streams (available from refineries and the HYDRISOM® process) has decreased markedly, and the price has risen. This change has been due to the ever increasing demand for alkylate for gasoline blending. 2-butene, when alkylated, gives an alkylate product with an octane number about 4 units higher than when 1-butene is alkylated. Since alkylate possesses high octane, is sulfur and aromatics free, and has a low vapor pressure, it has become the highest value blendstock for gasoline. Thus, the amount and purity of 2-butenes available for sale has decreased substantially.
Presently, 2-butene sells for a slight premium to 1-butene. However, thirty years ago, 1-butene sold for a slight premium to 2-butene. Furthermore, in the past 25 years, the demand for 1-butene as a comonomer for polyethylene has grown tremendously, and many companies have built ethylene oligomerization plants to meet this and other alpha olefin demand. High purity 1-butene with less than 100 ppm butadiene is now readily available at low cost providing another feedstock from which 2-butene product can be produced.
Therefore, there is a need in the chemical industry for an efficient process for isomerizing 1-butene to 2-butene. In particular, a catalyst and conditions that allow for extended catalyst run lengths (minimal catalyst deactivation) while employing an acidized clay catalyst has not been thought possible until now This invention provides a viable technology for that purpose.
Disclosure of other acidic catalysts for double bond isomerization have been reported; however, these catalysts are more expensive and less tolerant of extremes in operating conditions than the acidized clay catalysts disclosed here.